Plant pests moved into or through the United States, or interstate, must be free of soil, except when the Deputy Administrator approves in the permit the movement of soil with the plant pest. Subject to this exception, only approved packing materials are to be employed in the shipment of plant pests. Approved packing materials for the movement of plant pests under this part will be prescribed in administrative instructions or approved in specific cases by the Deputy Administrator. Such actions will be coordinated with and may supplement any requirements of the Post Office Department governing packing and packaging of any materials for movements covered by the postal laws and regulations. All containers shall be stoutly constructed so as to prevent breakage in transit and danger of plant pest dissemination and shall be labeled in accordance with § 330.211. The Deputy Administrator may allow the movement of host materials with plant pests under permits when they must necessarily accompany the pests, although such movement is otherwise barred under the Plant Protection Act.